One type of conventional brake control device is disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 61-160343 published on Jul. 21, 1986. This conventional brake control device includes a master cylinder for generating a hydraulic braking pressure in response to depression of a brake pedal, hydraulical pressure chambers provided in the master cylinder, a plurality of wheel cylinders communicating with the hydraulic pressure chambers via a plurality of hydraulic circuits, and an anti-lock control apparatus interposed in the hydraulic circuits. The anti-lock control apparatus includes a hydraulic pump driven by an electric motor, a reservoir and a changeover feature for selectively changing at least between a first condition in which an increase in the pressure of each wheel cylinder is permitted and a second condition in which a decrease in the pressure of each wheel cylinder is permitted in response to the locking condition of the road wheels.
In this conventional brake control device, however, since the hydraulic pump is driven by the electric motor, the size of the hydraulic pump may have to be increased and the size of the brake control device may also have to be increased. As a result, this conventional brake control device is restricted by space when the brake control device is equipped on vehicles. Furthermore, the operational sound of the electric motor caused by its rotation and operation is transmitted into the interior of the vehicle as undesirable noise.